Fourth seed Elena Dementieva admitted she was not ready physically for the French Open after being bundled out of the tournament.
The Russian, 27, won the first two titles of the season - in Auckland and Sydney - before making the semi-finals at the Australian Open, but her form has dipped since then.
She has been far from her best at Roland Garros and was lucky to get through the second round, when opponent Jelena Dokic was forced to retire through injury when a set and a break up.
Dementieva failed to make the most of that reprieve as she was beaten 6-3 4-6 6-1 on Philippe Chatrier court by another Australian, Samantha Stosur, who is a doubles specialist.
Dementieva said: "I just feel I'm far away from being in the right shape. I don't feel I could perform any better.
"I was not ready to play at the level I want to play. I was trying to be positive and fight for every match, but it's a very physical game when it comes to clay so it's not good for me.
"I'm just getting older, I guess. I have to work on my physical condition to get in better shape."
Stosur, the 30th seed, makes the fourth round at Roland Garros for the first time in singles. She won the women's doubles here in 2006 with Lisa Raymond.
"If I can keep playing the way I have been, anything is possible," said Stosur, who will next play France's Virginie Razzano.
"I felt good out there. I wasn't too nervous or anything."
Razzano is the second Frenchwoman to make the fourth round, along with Aravane Rezai, thanks to her 7-5 7-5 victory over Tathiana Garbin.
Dementieva's compatriot Svetlana Kuznetsova had no such problems on Suzanne Lenglen court.
The seventh seed demolished Hungarian Melinda Czink 6-1 6-3 and has only dropped 11 games all tournament.
She is the only player to have defeated Dinara Safina, the favourite for the title here, on clay this season - in the final in Stuttgart at the start of May - and she is delighted with her current form.
"I don't know why it's just all happened," the runner-up at the French Open in 2006.
"I have been working hard and I love to play on clay. My game is very effective playing on clay.
"I'm not thinking about my (title) chances but I know I can play great. The main thing is to keep focused."
Kuznetsova next plays 12th seed Agnieszka Radwanska, the Pole who beat Kateryna Bondarenko 6-2 6-4 today.
Elsewhere, 24th seed Aleksandra Wozniak was a 6-2 3-6 6-3 winner over Lourdes Dominguez Lino and will now play either Serena Williams or Maria Jose Martinez Sanchez.
In the other half of the draw, ninth seed Victoria Azarenka set up a last-16 meeting with reigning champion Ana Ivanovic after beating 22nd seed Carla Suarez Navarro 5-7 7-5 6-2.
The pair resumed this afternoon after finishing at one set all last night.